Tech Tips

jeep oliveCan’t Get No Satisfaction

This is probably not a vehicle question, but I hope you will answer. I am a Vietnam vet. When I was in Vietnam, I installed an 8-track player in the M37 I drove. I recently bought a 1966 M37 to restore as “my” Vietnam truck and installed a NOS 8-track player that I bought on Ebay to make it complete. It worked fine at first, but now it is playing the tapes too fast, and Mick Jagger sounds like Alvin the Chipmunk. Is there an adjustment for tape speed or is the unit just going bad because it’s old?

Thank you for your service. Did a tape get “eaten” just before the unit began playing too fast? If so, check the capstan. There may be several layers of the broken tape wrapped around it. This will speed up the playing.

By the way, it’s seldom the fault of the player if tapes get eaten. The  tape itself, if not subjected to temperature extremes or otherwise damaged, will last indefinitely. What usually happens is the tape breaks where it’s joined by the magnetic sensor strip (what triggers the player to change tracks) because the strip has deteriorated from age. This material is available from online sources. You should never play any vintage 8-track tape – even if it’s still sealed in its original wrapper – without first replacing the sensor strip. Likewise, you should check the condition of the foam pads and the rubber tape drive wheel. Replace them if necessary – and it is usually necessary.

Keep It Clean

Automobile polishing compound will quickly and thoroughly clean your vehicle’s windshield and window glass of old crusted stuff, bug splats, and paint overspray. It also works great on mirrors, reflectors, and head and tail light lenses. Car wax will brighten and preserve plastic lenses.

MUTT Mystery

Some M151s exhibit a mysterious little problem when idling: Sometimes the engine simply shuts off as if someone had flipped a switch, but it can usually be started again instantly.

If this has been happening to your MUTT, check the fuel safety shut-off switch. It is set to kill the electric fuel pump if the engine oil pressure falls below 10 psi.

Of course, check your engine oil pressure too, and make sure it isn’t actually dropping below 10 psi at idle, especially when it’s hot.

Resistance Is Not Futile

I’m converting my U.S. Navy M606 from 6- to 12-volts. I have a question about what coil to use. One kind needs an external resistor, but another kind doesn’t. Which kind should I use?

Basically, there are two common types of 12-volt ignition coils. One type has a 3-ohm internal resistor and is often used without an external ballast resistor. The second common type has a 1.5-ohm internal resistor and is generally used with an external ballast resistor. If so, it should be wired with an extra wire on the “+” terminal that will feed it a full 12 volts when the starter is cranking – usually from the starter solenoid. If not wired this way, you may have problems getting the engine started.

Some people have used 1.5-ohm coils without an external resistor, but the coil may become extremely hot in operation and will probably fail prematurely. While it is normal for coils to heat up, they should never become too hot to touch. Using a 1.5 ohm coil without an external resistor may also cause burned distributor points.

In either case, buy a good quality coil. There are a lot of cheapies on the Web these days which may only last a few months (if that) as well as causing other problems such as hard starting and / or engine misfiring. On the other hand, good quality coils often outlast the life of a vehicle.

‘Mog Wheels On A Wagon?

I have a Dodge WC 300 Power Wagon. I was looking at a Unimog recently and noticed that it seemed to have the same type of 6-bolt wheels. Those wheels and tires would look great on my truck, but are they the same lug pattern?Max

I believe that both the six-bolt Dodge and Unimog wheels will, indeed, interchange. The pattern should be the same – six on 7-1/4” center – but do some checking. Or, if possible, try to actually switch a wheel before making any purchases.

Which Way Did They Go?

I replaced the oil seals in my M37’s transfer case, but now I’m not sure which way the oil grove goes in the retainer? Up or down? J. Mendez

Such groves almost always face down so that oil drains back into transfer case or transmission instead of collecting around the seal and leaking out.

Hiding HMMWVs

In your article about HMMWVs in MV issue #103, you said it was a myth that HMMWVs were parked underwater to hide them. Why not? They are waterproof vehicles. – Don Langley

A better term would be “water resistant vehicles” similar  to many watches being advertised as “water resistant” rather than “waterproof.” The same would apply to all M-series vehicles, not just HMMWVs.

Even if fitted with a fording kit, driving a vehicle under deep water is considered a last-resort event. It’s a very stressful ordeal for the vehicle and meant to be over with as soon as possible.

Despite sealed dashboard instruments, lights and switches, as well as special gaskets and O-rings in air-cleaners, carburetors, starters and generators/alternators, the majority of seals and gaskets on M-series vehicles’ engines, transmissions, transfer cases and axles are of the conventional type. They are designed to keep oil and other fluids from leaking out , not to prevent water from leaking in. In other words, these gaskets are meant to withstand pressure from within, not from without.

Also, the special seals and gaskets on M-series vehicles, including the battery caps, are not designed to withstand submersion for long periods of time. In addition, most M-series vehicles have a fording valve that uses engine crankcase pressure to pressurize their transmissions, transfer cases and axle differentials when fording, so their engines must be running to provide this pressure.

Simply put, there are just too many places for a vehicle to leak. If an M-series vehicle – including a HMMWV – was parked under water for any length of time, you would likely find its engine, transmission, transfer case, and axles, as well as its batteries and possibly its fuel tank, full of water when you attempted to start it.

In Too Deep

I just installed a deep-water fording kit on my 1954 M38A1. I want to try it out. Are  there any precautions to take?A. Ross

The best precaution would be not to do it. Most smart people who drive off-road or out in the bush and who don’t have breakdowns or get stuck, use the philosophy of, “do I really need to go there?” before attempting to climb a mountain or cross a river.

Aside from asking yourself that question, you should get a manual that covers the procedures for deep-water fording your Jeep. Driving any vehicle under deep water is not a casual event: It requires proper preparation as well as service after the fact… such as checking the engine, transmission, transfer case, axles, batteries, fuel tank, and brake master cylinder for water when you’re back on dry land.

Also keep in mind, that just because you recently installed a fording kit, that’s no guarantee that the seals, gaskets and O-rings on your M38A1 are in good enough shape to withstand deep water pressure.

If, in spite of this advice, you want to go ahead with this adventure, you should have another vehicle standing by that is capable of rescuing your Jeep. Also, be sure to remove the fan belt, because the fan blades may be bent forward and cut into the radiator from trying to pull water instead of air.

Geared up

Are those higher gear sets for M37s and M715s worth the price?George Finney

That depends on how you use your vehicle. The gear sets are worth the price if most of your driving is on-highway.

We used to be able to find complete third-members in wrecking yards from Dodge 1-ton civilian trucks that would replace the units in M37s. These  allowed a comfortable cruising speed of 55 mph. This, I believe, is what the conversion kits offer.

You do lose some on-highway power, though I had the aforementioned gear sets in an M37 and liked them very much. Also, since you have higher-speed axles, you can get better speed from all the transmission gears. So, even if you have to shift down on steep hills, you can still go faster. Off-road performance is not affected much since you have a low range in the transfer case.

I don’t know about the new kits, but the old civilian sets were slightly weaker than the M37s orginal units, which might be something to consider if you use your truck for heavy hauling or in extreme off-road conditions.

Squelching The Squeal

The throw-out bearing on my Kaiser M715 has started to squeal when I step on the clutch. It doesn’t do it all the time, but the thought of having to pull everything apart to replace it is not very appealing.

I know that some tractors and heavy equipment have throw-out bearings that can be greased. If I do have to pull everything apart, could I install one of these bearings? – Jared

If you are a good mechanic, jou can do just about anything; but you might want to try something simpler. I once installed an M715 engine, transmission, and transfer case in a 1947 Willys pickup. The throw-out bearing started to squeal a year later. Not wanting to pull the transmission to replace a twenty-dollar item, I removed the clutch housing cover and drilled a small hole in the throw-out bearing’s case.

This hole was just large enough to insert a needle-tip attachment on my grease gun. I slowly pumped some high-temp wheel bearing grease into the bearing, rotated the bearing by hand, and repeated this process several times to distribute the grease evenly within the bearing’s shell. I then wiped the bearing’s shell with a rag soaked in gasoline to clean off excess grease, and finally pressed a small dab of silicone gasket sealer over the hole.

I drove that truck from California to Alaska and back, and the bearing was still silent and working fine when I sold the truck several years later.

Less Noise, More Fire?

Would spraying my M715’s fire wall and underside of the floor pan cut down engine noise? Also, would there be any danger of this stuff catching fire in the engine compartment?T.T.

It would soften the noise slightly, but not to any significant degree. Rubber floor mats and acoustic padding on your firewall would work much better.

I sprayed the fire wall of a 1947 Willys pickup with undercoating, then a year later I had to use a cutting torch when installing a different engine! While different brands of undercoating probably have different formulas, the stuff I used didn’t catch fire – even when subjected to the cutting torch’s extreme heat.

Diddling Diodes

If the fuel solenoid diode (NSN 5961-01-180-5634) burns out in your HMMWV, TACOM LCMC recommends replacing it with a NSN 5961-01-593-3791 diode. This provides better electrical protection.

You can tell the two diodes apart by the protective shrink sleeve on each. The new diode has a blue sleeve. The old diode’s sleeve is black. The old diode is still being used, but it should only be applied to the horn circuitry for vehicles with serial number 255269 and above that have the Smart Start System.

So both diodes will be added to the HMMWV parts TMs in a future update. The main reason for the original diode’s failure is that vehicles are being improperly slave started. That causes a transient voltage spike that can damage other electrical components as well as the diode. – PS Magazine

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